Cooling System: Description and Operation

Temperature Sensor At Radiator Outlet

Temperature sensor at radiator outlet
The temperature sensor is clipped into the coolant line at the radiator outlet.
The temperature sensor converts the temperature of the coolant after the radiator into an electrical value (resistance). To do this, a resistance with negative temperature coefficient (NTC) is used. The coolant temperature is the measured variable for the following calculations, for example: Fuel injection rate and nominal idle speed.

Functional description
A temperature-dependent electrical resistor is used for temperature sensing. The circuit contains a voltage divider where the resistance can be measured depending on the temperature. A temperature is converted using a characteristic curve specific to the sensor. An NTC resistor is installed in the temperature sensor, whose resistance value drops when the temperature increases.







The resistance changes from 167 kOhms to 150 Ohms depending on temperature, which corresponds to a temperature of -40 °C to 130 °C.

Structure and inner electrical connection
The temperature sensor is connected via a 2-pin plug connection.
The resistor is part of a circuit as a voltage divider that is supplied with 5 volts by the engine control.







Characteristic curve and setpoint values
The electrical voltage at the resistor is dependent on the coolant temperature. A table that specifies the temperature associated with each voltage value is stored in the engine control. This compensates for the nonlinear relationship between electrical voltage and temperature.







Observe the following setpoint values for the temperature sensor at radiator outlet:

Size Value
Nominal resistance at 25 °C 2252 Ohms ± 1.5 %
Power consumption 1 mA
Response time 15 s
Temperature resolution ±1 °C
Maximum output current 20 mA
Temperature range -40 °C to 150 °C

Diagnosis instructions

Failure of the component
If the temperature sensor at radiator outlet malfunctions, the following behavior is to be expected:
- Fault entry in the engine control unit
- Emergency operation with substitute value

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